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How do I make an anti-static wrist strap, /w resistor, to work on computers? Answered


An antistatic wrist strap is a useful thing to use when handling static sensitive devices like computer cards and ram, or static sensitive chips. Touching the computer case is only useful if it is plugged in to the mains with a grounded pin. If it is not, you do not get rid of any static charge buildup. To make your own, you need to have metal contacting your body through a metal bracelet. You then wire this bracelet through a 1 Megaohm resistor to a crocodile clip. YOU MUST USE THIS RESISTOR just in case you accidently make contact with a live wire. The crocodile clip is then clipped to the earth or ground point.

It seems a bit contradictory to dismiss grounding yourself on the case as ineffective if it's not plugged in, and to warn about accidentally touching live wires...

Computers should be unplugged before they are worked on.


I said that "Touching the computer case is only useful if it is plugged in to the mains with a grounded pin." If the case is NOT connected, then touching the case will NOT get rid of static charge. It will put you at the same potential of anything in the case, as replied to NachoMahma above.

A plugged in computer HAS the possibility that you will come in to contact with a live wire. Sorry, I seem to misunderstand where the contradiction is.

For the record, I work on computers plugged in, but with the power to the mainboard disconnected, or with the power plug in, but the power off. This ensures that the case is at ground potential, AND touching the case will get rid of any static charge.

So you're working on case-earthed computers, with yourself earthed too? The contradictory-seeming part was just the warning about "YOU MUST USE THIS RESISTOR just in case you accidently make contact with a live wire" which you're obviously not going to do. (I've never used a strap, never known or seen anyone else use one either - nothing fried) Still it doesn't hurt to be cautious. L

If you are working on a grounded case, it IS quite safe to get rid of static charge by touching the case. Did I say otherwise?

I thought it was pretty clear in the last paragraph when I said "To make your own.." (anti static strap I mean, since that was the question) you must not omit the resistor. If you wear the strap on your left hand, and your right hand makes contact with a Live wire, too much current might flow through your heart, and kill you. The resistor limits current to ground. Again, to make your own... The Live does not even have to be from inside the case. You could pick up a faulty hot air gun to shrink some sleeving for example.

But since the question was to make one, I'd expect the person to want to use it. That person is now grounded. So it comes down to this : if you are going to make your own antistatic wrist strap, make sure it a safe one. Bold and in caps this time : PLEASE DO NOT OMIT THE RESISTOR. THE STRAP IS UNSAFE IF YOU DO OMIT IT. Where is the contradiction?

Anyway, I think this back and forth belongs in the forum, not in the answer section, so I won't post here on this again. Anyone reading should be able to make up their own mind from all that has been written.

I agree with your last comment, but I wouldn't have spent so much text getting there. L

Whoops! Yeah, sorry about that. Just that you seemed a bit dense to understand the issues at hand. My apologies to you lemonie. Should have just answered like you did - "I don't see much point." And here I was trying to answer the question. Lesson learned. Thanks for the guidance, will not repeat it in the future.

I think we both know what we're doing, but we do things differently (and I play with live mains...) Later dude L

You play with live mains?! Wow, I do too. I once blew up this 3 phase system and shut down half this 40 story building. :-) Now I can laugh about it, but when it happened, it would be enough to turn you religious.... I still keep those enormous fuses as a reminder of what NOT to do! Cheers. Aargh, we're doing this in the "answers" section, not the forum. Ok, this time I'm really not going to post anymore to the answers section!!

> Touching the computer case is only useful if it is plugged in . Not entirely true. It will put you and the computer at the same potential. This may not be ground potential, but deltaV is required for damage to happen. . Not as good as a strap and proper grounding, but much better than nothing.

Correct about the computer and you being at the same potential. But the moment you pick something off the table top, or put something down, there will be a dV, and the possibility of frying the component/card.

Buy one off DX.

I've never use these, I don't see much point. If you touch the case periodically you achieve much the same benefit (if there is one) L